1. Field of the Invention
The present invention relates to a grating image having one or more grating fields, each of which includes an electromagnetic radiation-influencing grating pattern comprising a plurality of grating lines, the grating lines being characterized by the parameters orientation, curvature, spacing and profile. The present invention further relates to a method for manufacturing such a grating image, as well as a security element, a security paper and a data carrier having such a grating image.
2. Description of the Prior Art
To ensure the authenticity of credit cards, banknotes and other value documents, holograms, holographic grating images and other hologram-like diffraction patterns have been used for several years. In general, in the field of banknotes and security, holographic diffraction patterns are used that can be manufactured by embossing holographically produced grating images in thermoplastically moldable plastics or UV-curing lacquers on foil substrates.
True holograms are created by illuminating an object with coherent laser light and superimposing the laser light scattered by the object with an uninfluenced reference beam in a light-sensitive layer. So-called holographic diffraction gratings are obtained when the superimposed light beams in the light-sensitive layer consist of spatially extended, uniform, coherent wave fields. Through the action of the superimposed wave fields on the light-sensitive layer, for example a photographic film or a photoresist layer, a holographic diffraction grating is created there that can be preserved in the form of light and dark lines in a photographic film or in the form of peaks and valleys in a photoresist layer. Since, in this case, the light beams were not scattered by an object, the holographic diffraction grating produces merely an optically variable color impression, but no image representation.
From holographic diffraction gratings, it is possible to produce holographic grating images, not by covering the entire surface of the light-sensitive material with a uniform holographic diffraction grating, but rather by using suitable masks to cover, in each case, only portions of the recording surface with one of multiple different uniform grating patterns. Such a holographic grating image is thus composed of multiple grating fields having different diffraction grating patterns that normally lie next to one another in a planar, strip-shaped or pixel-like design. With such a holographic grating image, it is possible to depict numerous different image motifs through suitable arrangement of the grating fields. The diffraction grating patterns can be produced not only through direct or indirect optical superimposition of coherent laser beams, but also by means of electron lithography. Frequently, a sample diffraction pattern is produced that is subsequently translated into a relief pattern. This relief pattern can be used as an embossing die.
From publication DE 102 26 115 A1 are known grating images that are not composed of individual pixels or strips, but rather in which large grating fields that are perceptible with the naked eye are covered with a uniform grating pattern. In this way, since unexposed empty spaces are avoided and only a few discontinuous transitions are present between the large-area grating fields, a high light intensity of the grating images is achieved.
Based on that, it is the object of the present invention to further improve grating images of the kind cited above, and especially to create grating images having new optical effects and/or to further increase the counterfeit security of the grating images while preserving the existing advantages.